In an automobile of front-wheel drive for example, an engine set at the front of the vehicle's body generates torque, and a differential receives and distributes this torque to right and left front wheels. In a case of a four-wheel drive vehicle, a power takeoff unit (PTU) is, in general, in combination with a transmission with a differential, used to take off torque in part and transmit it to rear wheels.
A construction that time-limitedly switches its drive mode into a two-wheel drive mode is often applied even to a four-wheel drive vehicle loaded with a PTU. In this case, one or more clutches for temporarily cutting off power transmission are inserted into any part of a powertrain system from the PTU through the rear-differential. When one of the clutches gets disengaged, the engine does not bear rotation of part of the transmission downstream relative to the concerned clutch and therefore this construction is advantageous in improvement of energy consumption.
Japanese Patent Unexamined Application Laid-open No. 2012-193779 discloses a related art. To maximize energy consumption improvement, it is advantageous to provide at least one of the clutches to an upstream section in the transmission path of the torque, and therefore, in the example of Japanese Patent Unexamined Application Laid-open No. 2012-193779, a clutch is incorporated in a PTU. The PTU is inevitably designed to have a complex structure, which causes some problems. For example, its assembly inherently becomes troublesome and accordingly its disassembly also becomes troublesome, thereby causing problems in maintenance. Further, modification of the construction of the PTU is difficult to realize by partially changing the construction and instead it is necessary to replace the PTU as a whole with a PTU structured in a desired construction. The device described below has been devised in light of these problems.